Each population of nerve cells depends on specific type of growth factors.

Many growth factors continue to be synthesized in the ADUKT brain, adult neurons apparently not as dependent on growth factors for their survival, but other important properties may be regulated (synaptic function, sprouting of terminals)

Major Questions: are neurodegenerative disease caused by decreased secretion of growth factors

Extracellular Matrix (ECM)

molecules provide an adhesive substrate for growing nerve fibers

examples: collagens, fibronectin, laminins

Cell adhesion Molecules:

(CAMs) on cell membranes cause adhesion and fasciculation

Examples: NCAM, L1, cadherins (Ca++ dependent)

Signals that guide nerve fibers

are not recognized also to be important in guiding the growth ob flood vessels to establish the vascular pattern for the body!

Development of the cerebral hemispheres and cortex: weeks 8-36

Adult cerebral hemispheres: cell bodies are located in a thin region of the outer cortex (gray matter), axons are located deeper in a fiber layer (white matter), and some nuclei (cell bodies) are buried deep in the fiber layer

Cortex is layered based on the types and positions of nerve cell bodies with regional differences: neocortex has 6 layers.

Embryonic brain

is composed of thin telencephalic compartments containing scattered cells surrounding the internal space that will become the ventricles

The hemispheres development

they develop by proliferation and migration of neuroblasts in the wall of the embryonic telencephalic vesicles. This process

1) increases the mass of the telencephalic compartments

2) allows neurons to migrate towards the pial surface where they form the cortex

3) results in the formation of cortical layers for information processing

Neuroepithelial cells proliferate in a zone (subventricular zone) adjacent to the lateral ventricle of the telencephalic vesicle.

Cell bodies of differentiating neurons migrate toward the pial surface either on their own or along fivers of radial glial cells that span the width between ventricle and pial surface

Subventricular zone

remains an important area in some regions of the adult brain where neuronal stem cells continue to form neurons even in adults.

These areas have potential for harvesting stem cells for use in repairing damaged areas of the brain